setreuid(2) set real and effective user ID's


Lb libc


In unistd.h Ft int Fn setreuid uid_t ruid uid_t euid


The real and effective user IDs of the current process are set according to the arguments. If Fa ruid or Fa euid is -1, the current uid is filled in by the system. Unprivileged users may change the real user ID to the effective user ID and vice-versa; only the super-user may make other changes.

If the real user ID is changed (i.e. Fa ruid is not -1) or the effective user ID is changed to something other than the real user ID, then the saved user ID will be set to the effective user ID.

The Fn setreuid system call has been used to swap the real and effective user IDs in set-user-ID programs to temporarily relinquish the set-user-ID value. This purpose is now better served by the use of the seteuid(2) system call.

When setting the real and effective user IDs to the same value, the standard Fn setuid system call is preferred.


Rv -std setreuid


The current process is not the super-user and a change other than changing the effective user-id to the real user-id was specified.


The Fn setreuid system call appeared in BSD 4.2